Create Pane/PaneContainer through RootView
Create Pane/PaneContainer through RootView

This requires having no direct dependencies on these classes and instead
exercises tabs as if they were created as a RootView-managed pane.  This
mirrors more closely the actual behavior since the package main relies
on RootView::eachPane as the entry point for each tab bar view.

harai/tabs,pombredanne/tabs,atom/tabs,acontreras89/tabs